Field Notes Journal

UK Bat Emergence Time Calculator

Emergence Times and Hibernation Periods

Hibernation in UK bats does not follow a fixed calendar. It is influenced by temperature, weather, and food availability, and some species may still show activity on mild winter nights.

Even so, there are well-established typical seasonal windows that are useful when planning observations. The table below summarises typical emergence times relative to sunset, together with broad hibernation periods, for a selection of UK bat species.

Common Name Scientific Name Emergence Hibernation Starts Hibernation Ends
Brandt's Myotis brandtii +20 to +60 min Oct – Nov Mar – Apr
Brown Long-Eared Plecotus auritus +30 to +90 min Oct – Nov Mar – Apr
Daubenton's Myotis daubentonii +10 to +40 min Nov Mar – Apr
Greater Horseshoe Rhinolophus ferrumequinum +20 to +60 min Oct Apr – May
Lesser Horseshoe Rhinolophus hipposideros +10 to +40 min Oct Apr – May
Natterer's Myotis nattereri +20 to +60 min Oct – Nov Mar – Apr
Noctule Nyctalus noctula -10 to +10 min Oct – Nov Mar – Apr
Common Pipistrelle Pipistrellus pipistrellus +5 to +30 min Oct – Nov Mar – Apr
Common Pipistrelle Pipistrellus pipistrellus +10 to +40 min Oct – Nov Mar – Apr
Soprano Pipistrelle Pipistrellus pygmaeus 0 to +30 min Oct – Nov Mar – Apr
Soprano Pipistrelle Pipistrellus pygmaeus +10 to +40 min Oct – Nov Mar – Apr
Whiskered Myotis mystacinus +20 to +60 min Oct – Nov Mar – Apr

Notes

  1. Emergence is expressed as minutes relative to sunset. Negative values indicate times before sunset; positive values indicate times after sunset.
  2. Hibernation periods are approximate seasonal windows rather than fixed calendar dates.
  3. Winter activity may still occur during mild spells, particularly in some species.

Using the Calculator

This calculator builds on the annual NOAA Solar Calculations spreadsheet, adding species emergence times and hibernation periods to estimate likely emergence windows for each day of a selected year.

Tab Name Contents
NOAA Sunset Calculator The original NOAA solar calculation sheet
Species Emergence - Field Notes Species definitions, including common name, scientific name, emergence timing, and hibernation period
Emergence Times - Field Notes The annual emergence-time view for 1 January to 31 December for the selected year

Steps

  1. On the NOAA Sunset Calculator sheet, enter latitude, longitude, time zone 1, and year.
  2. Copy the species name from the Species Emergence - Field Notes sheet.
  3. Paste the species name into cell A2 of the Emergence Times - Field Notes sheet.
  4. The annual emergence table will recalculate for that species, with hibernation periods indicated.

Attribution and Provenance

The solar calculations in this workbook are based on the NOAA Solar Calculations spreadsheet provided by the National Oceanic and Atmospheric Administration (NOAA). The NOAA sheet is included in unmodified form as the workbook’s first tab.

Species emergence times and hibernation periods are drawn from a synthesis of widely available UK bat field guides and acoustic survey references.

The selection, structuring, and interpretation of this information, together with the design of the calculator and its presentation, are original to Field Notes Journal.

This workbook is not an official NOAA product and is provided here as a field-planning aid for recreational and observational use.

For the original NOAA calculator, see: NOAA Solar Calculation Details

Emergence times and hibernation periods presented here are a practical synthesis of widely available UK bat field knowledge. They should be treated as indicative planning guidance rather than fixed biological rules.

  1. The time zone should account for daylight saving time (DST) so, for example, in the UK BST is 1 and GMT is 0 ↩